Electromagnetic repulsion device actuating the movable contact member of a circuit interrupter

ABSTRACT

Electromagnetic repulsion device comprising a magnetic circuit energized by the current flowing through a circuit interrupter and an induction-plate which is movable with the movable contact member of the circuit interrupter. The abrupt rising of a fault current induces secondary currents in the induction-plate to vigorously expel the induction-plate from the air gap of the magnetic circuit in which it is normally located when the circuit interrupter is in the closed-circuit position so that the contacts are rapidly opened.

United States Patent [191 Terracol July 16, 1974 ELECTROMAGNETIC REPULSION DEVICE ACTUATING THE MOVABLE CONTACT MEMBER OF A CIRCUIT INTERRUPTER [75] Inventor: Claude Terracol, Grenoble, France [73] Assignees MERLIN GERIN Societe Anonyme, Grenoble, France 22 Filed: May 21,1973

21 Appl. No; 362,267

[30] Foreign Application Priority Data May 26, 1972 France 72.19239 52 us. c1. 335/1 6, 335 99 [5H Int. Cl. HOlh 77/02 [581 Field 0fSearch....... 335/16, I95, 99, 100, 147; 310/10, 14

[56] References Cited UNITED STATES PATENTS 2,916,579 12/1959 Kesselring et al 335/l l7 3,238,326 3/1966 Frey 335/195 3,281,733 10/1966 Jensen 335/99 3,663,903 5/1972 Kussy et al 335/16 Primary Examiner-Harold Broome Attorney, Agent, or FirmSteve r 1s Davis, Mil le r 8L Mosher [5 7] ABSTRACT Electromagnetic repulsion device comprising a magnetic circuit energized by the current flowing through a circuit interrupter and an induction-plate which is movable with the movable contact member of the circuit interrupter. The abrupt rising of a fault current induces secondary currents in the induction-plate to vigorously expel the induction-plate from the air gap of the magnetic circuit in which it is normally located when the circuit interrupter is in the closed-circuit position so that the contacts are rapidly opened;

12 Claims, 6 Drawing Figures PAIENIEDJULIBIHH I sum 1 or 4 Fig.5

PAIENIE JUL 1 6 I974 SHEET 3 OF 4 PATENTED m 1 6 m4 SHEET t [if 4 -Fig-6 ELECTROMAGNETIC REPULSION DEVICE ACTUATING THE MOVABLE CONTACT MEMBER OF A CIRCUIT INTERRUPTER This invention relates to circuit interrupters and more particularly to current-limiting circuit interrupters having high-speed opening means which are energized by the current flowing through the circuit interrupter.

In current-limiting circuit breakers the contacts are opened independently of the normal movable-contact operating mechanism (which may comprise an electromagnetic tripping relay'sensitive to the short-circuit current flowing through the apparatus) upon the occurrence of fault currents of predetermined value. The object is to rapidly develop a relatively high voltage drop in the circuit in which the interrupter is-inserted in order to limit the peak value of the expected shortcircuit current. To this end, a voltage-drop introducing arc must be initiated and developed between the separating contacts in extremely short time, typically of the order of a couple of milliseconds or less, depending on the value of the short-circuit current available. Clearly, the normal tripping devices cannot move the contacts fast enough during such small time intervals and'prior art current-limiting circuit interrupters have therefore been developed providing electrodynamic effects produced by the short-circuit current itself to bring about high-speed contact separation. Unfortunately, the design of the electrodynamically interacting parts, including the movable contact, of circuit interrupters of this kind raises problems which are difficult to overcome,

especially if the prospective currents are of high levels calling for relatively bulky conductors, some of which are movable.

Electromagnetic movable-contact operating devices have also been proposed. One of the devices of this kind has the movable contact itself disposed in the air gap of an energized magnetic circuit whereby the current flowing through the contact interacts with the magnetic field in the air gap to produce a Laplace force tending to move the contact. Such a system is simple and effective but impracticable in case of high ratedcurrent levels because of the bulkiness of the movable contact which calls for a relatively wide air gap increasing the reluctance of the magnetic circuit in a prohibitive way.

It is an object of the invention to provide an electromagnetic movable-contact actuating device of simple and reliable construction capable of producing high movable-contact opening forces under short-circuit conditions.

It is a related object of the invention to provide an electromagnetic movable-contact actuating device of high efficiency having a low-reluctance magnetic circuit in which the width ofthe operative air gap is small and relatively independent of the size of the movable contact.

It is a further object of the invention to provide a contact separating-device combining the effects of electromagnetic repulsion and attraction to open the- According to an aspect of the invention, the electromagnetic, repulsion actuating the movable contact member of a circuit interrupter is produced by currents which are induced in a relatively small induction-plate secured to the movable contact means and inserted in the air gap of a magnetic circuit energized by the very short-circuit current flowing through the circuit interrupter.

These and other objects, features and advantages of the invention may be more fully understood upon reading of the following description of some embodiments of the invention schematically shown in the accompanying drawings, in which:

FIG. 1 is a side elevation, partially in cross section of a device according to the invention;

FIG. 2 is a view taken through line II -'II of FIG. 1 looking in the direction of the arrows II II;

FIG. 3 is a side elevation of the movable contact means of another embodiment according to the invention;

FIG. 4 is a side elevation, partially in cross section of a third embodiment according to the invention;

FIG. 5 is a view taken through line V V of FIG. 4

looking in the direction of the arrows V V; and

FIG. 6 is a plan view taken through line VI-VI of FIG. 4 of the magnetic circuit. Referring now to the embodiment represented in FIGS. 1 and 2, there is shown the contact-means of a circuit interrupter (which is not further shown) comprising a translational movable bridging contact member 10 carrying a pair of opposed contacts 12 and 14 adapted for engagement with a pair of opposite stationary contacts 16 and 18 carried by a pair of currentsupply conductors 20 and 22, respectively. A generally loop-shaped magnetic circuit 24 surrounds the movable contact member 10 and has confronting pole faces defining a relatively small air gap 26. The contact member 10 carries a depending keel-shaped projection 28 so as to present a generally T-shaped cross section, as shown. The contacts 12 to 18 may be main or arcing contacts. A circuit interrupter comprising a combination of main and arcing contacts will be described hereinafter.

The movable contact member 10 defines a main current path for the current flowing through the circuit interrupter successively through the parts 20, 16, 12, 10, 14, 18 and 22 or vice-versa. The main current path in the embodiment shown is parallel to the plane of the paper of FIG. 1 and perpendicular to the plane of the paper of F IG. 2, as shown schematically by the current line carrying the arrow i in the embodiment shown, the movable contact member is guided for vertical translation as viewed in FIG. 1 but it will be understood that the invention is also applicable to pivotally mounted contact members. On the other hand, the contact pairs 12, 16 and l4, 18 may be replaced by a single contact pair, especially in case of a pivotally mounted contact member. It is to be noted that the total cross-sectional area of the main current path of the movable contact member 10, Le. the area of the bar-shaped upper part, is large relative to the area of the keel-shaped projection 28 of conductive material which constitutes an induction-plate cooperating with the magnetic circuit 24 and which extends in the air gap 26, at least as long as the circuit interrupter is in its closed-circuit position shown in FIG. 1. The elongated induction-plate 28 extends a length parallel and adja- 3 cent to the main current path and defines thus a path for secondary currents which is in shunting relation with the main path.

This device operates as follows:

In the normal closed-circuit position of the contact member 10 the current flows through the upper part of the contact member 10 along the main current path in the direction of the arrow i or in the opposite direction. The fraction of the current flowing through the induction-plate 28 is negligible. The current i, energizes the magnetic circuit 24 and generates a magnetic field inthe air gap 26 directed along the arrow B or in the opposite direction, depending on the direction of the instantaneous current. As soon as a short-circuit appears, the rapid rising of this current and the corresponding'rapid rising of the magnetic induction B in the air gap 26 induces secondary currents i in the induction-plate 28 whereby the return path of these loopcurrents merges with the main path of the current in the upper part of the current member 10 as shown-in FIG. 1. The value of the current i is of the same order as the value of the current i and the whole operates as a transformer of ratio 1:]. In fact, the result is as if the whole short-circuit current were initially deviated towards the induction-plate. Consequently, the current i in the induction-plate 28 interacts with the magnetic induction B to produce a force F directed perpendicularly to the instantaneous directions of the current lines i and of the magnetic field lines B. This force tends to expel the induction-plate upward from the air gap 26 thereby vigorously opening the contacts before the nor-,

mal tripping mechanism becomes operative. The small reluctance of the magnetic circuit 24'resulting from the small width of the air gap 26 provides a magnetic field of high value acting on the current lines in the induction-plate. The force F acts on a movable contact member having a small inertia thereby producing a high acceleration and a rapid opening of the contacts. The conventional electrodynamic effect due to the loopshape of the current flowing through the parts 20, 10 and 22 increases the force F.

FIG. 3 shows an embodiment in which the current lines of the secondary current i are canalized in order to increase the repulsion force F. The central part'of the induction-plate 28 carries a longitudinally extending slot or groove 30 and the shunt path is created by connecting the end portions 32 and 34 of the lower part of the induction-plate to the movable contact 10 defintute a unitary structure therewith. The active part of the current lines i is thus increased. The pole faces of the magnetic circuit may be coextensive with the shunt path 34, 28, 32 or overlap a part of the opening 30 to increase the magnetic coupling between the contact member 10 and the induction-plate 28. The opening may be filled with ferromagnetic material wrapped with electrically insulating material. The separation between the main and the shunt path may also be brought about by one or more parallel insulating layers.

The induction-plate 28 is preferably of conducting non-ferromagnetic material but it is conceivable to make the induction-plate of ferromagnetic material only in which case the useful force F is partially counterbalanced by magnetic attractive forces.

- FIGS. 4 to 6 represent another embodiment of the invention.

A movable contact member 10 carries again a pair of movable contacts 12 and 14 which cooperate with a pair of stationary contacts 16 and 18 carried by a pair of stationary supply conductors 20 and 22, respectively, as in the embodiment of FIGS. 1 and 2. The

movable bridging contact member 10 carries again a keel-shaped induction-plate 28 extending longitudinally in the air gap 26 of a magnetic circuit 38, at least as long as the contacts are in the closed-circuit position thereof shown in FIGS. 4 and 5. The magnetic circuit 38 comprises a generally rectangular yoke 39 of ferromagnetic material (FIG. 6) the medianv portion of which is bridged by a pair of upper ferromagnetic trans verse plates 36 and 36' defining the air gap 26 between their confronting pole faces. The left portion of the magnetic circuit is energized by thetraversing conductor 20 and the right side by the conductor 22so that the magnetic fluxes produced in the air gap 26 are added together. A pair of arcing contacts 40 and 42 is associated with the main contacts 16 and 12 and a pair of arcing contacts 40 and 42 cooperates with the main contacts 18 and 14 (from now on the right-hand elements corresponding to the symmetrical left-hand elements are designated by the same reference characters marked by a prime). The stationary arcing contacts and 4 0 are supported by brackets 46 and 46', respec tively, carried by the respective conductors 20 and 22. If desired, the arcing contacts 40 and 40 may also be mounted in a semistationary manner on the conductors so as to permit a limited displacement of these contacts in the direction of the opening movement of the associated contacts 42 and 42 under the action of appropriate springs (not shown) in a well-known manner. The movable arcing contacts 42 and 42' are mounted on support pins 48 and 48 which are slidably supported and guided by a bar 50 secured to the movable contact member 10. Pins 48 and 48 carry stops 52.and

52 to limit the movement of the contacts 42 and 42' in the direction. of the stationary, or semistationary contacts 40 and 40'. Compression springs 54 and 54 bearing on rigid arms 56 and 56 and on the pins 48 and 48 urge the movable contacts 42 and 42 in the direction of the fixed contacts. The arms 56 and 56' are carried by a plate 58 having two holes accomodating two lost-motion bolts 60 and 60 secured to the assembly of the bar 50 and of the movable contact member 10. Upper stops 62 and 62 on the bolts 60 and 60' limit the movement of the plate 58 away from the movable contact member 10 and a pair of compression springs 64 and 64' tend to take up the lost motion and to urge the plate 58 against the stops 62 and 62'.

The normal opening and closing mechanism of. the circuit interrupter comprises a control plate 68 the vertical (as viewed in FIGS. 4 and 5) sliding movement of which is in turn controlled by a toggle mechanism 78 having one end pivotally mounted on a stationary axis 79 and another end pivotally mounted on a lug 81 secured to the plate 68. The stretching and collapsing movement of the toggle mechanism 78 is controlled in any well-known appropriate manner as by a manual or automatic tripping mechanism (not shown). A pair of guide rods and 80' on the plate 68 traverse holes in plate 58 to guide the translational movement of the latter relative to the control plate 68 and a pair of stops 83 and 83' secured to the lower part of the guide rods 80 and 80' limit the movement of the plate 58 away from the control plate 68. A compression spring 66 surrounding a spring guide 67 secured to the control plate 68 tends to move the plates 68 and 58 away from each other.

The plate 58 is rigidly connected to a lower armature plate 72 by a pair of rods 70 and 70 which traverse the plates 36 and 36 and the yoke 39, and chamfered edges 82 and 82' of the armature plate 72 define with corresponding chamfered edges 86 and 86 of the magnetic circuit 39 a pair of air gaps 74 and 74 in the closed-circuit position of the apparatus shown in FIGS. 4 and 5.

Finally, a pair of arc chutes or arc extinguishing chambers 76 and 76' shown in FIG. 4 only is associated with the arcing contacts 40, 42 and 40, 42', respectively, to permit a rapid extinction of the arcs drawn between these contacts.

This interrupter operates as follows:

In the shown closed-circuit position of the interrupter the current flows through the supply conductor 20; the contacts l6, 12; the main path (as described hereinbefore) in contact the contacts 14, 18; and the conductor 22, successively, or vice-versa. A negligible part of the current flows through the arcing contacts 40, 42

and 40, 42' also with the additional help of springs 54 and 54, respectively. The current flowing through the supply conductors 20 and 22 energizes the magnetic circuit 38 and generates a magnetic field in the air gaps 74 and 74' tending to attract the armature 72. In normal service this force is too small to overcome the opposing force exerted by the spring 66 which maintains the contacts in closed position.

At the appearance of a short-circuit current the apparatus operates in different manners according to the value of the current. The occurrence of a short-circuit current of moderate value but exceeding a predetermined value causes the force of attraction of the armature 72 to surpass the opposing force of the spring 66. As a consequence the armature 72 is attracted by the magnetic circuit 38 and the plate 58 lifted. The plate 58 takes up the lost-motion and abuts thereafter on the stops 62 and 62 thereby also lifting the bar 50 and the movable contact member 10. The main contacts l2, l6

and l4, 18 separate without drawing an are as the arcing contacts remain closed for the time being. Continuing its stroke, the plate 58 and the assembly 50, 10 moving together take up the lost-motion 84, 84 to separate the arcing contacts 40, 42 and 40, 42', respectively drawing two series-connected arcs therebetween, the arcs being urged into the arc chutes 76 and 76' to be extinguished in due course. The current induced in the induction-plate 28 is too small to have an appreciable influence. In the mean time the toggle joint 78 is actuated by the normal circuit-breaker tripping mecanism and the contacts are maintained in the open-circuit position.

At the appearance of a major fault current, the current induced in the induction-plate 28 upon a rapid rising of the short-circuit current suffices to lift the assembly 10, 50 against the opposing action of the springs 64 and 64. The inertia of the moved mass is relatively small and the opening movement is accelerated by the electrodynamic forces resulting from the loopconfiguration of the supply conductors and the bridging contact. The main contacts open and transfer the current instantaneously to the arcing contacts which separate then to draw arcs which are immediately transferred to .the arc chutes 76 and 76. During this initial time interval the plate 58 remains in position. Subsequently, if the short-circuit current persists, the attraction of the armature 72 becomes effective to move the plate 58 upward to maintain the arcing contacts in open-circuit position pending the action of the normal tripping mechanism.

While there have been described only some preferred embodiments of the invention, it will be understood that numerous variations and modifications may be made without departing from the spirit of the invention. Therefore, the invention is to be limited only by the appended claims.

What is claimed is:

1. An electromagnetic repulsion device causing under predetermined fault current conditions the separation of the separable contact means of a circuit interrupter by imparting motion to a movable contact member of said contact means, said movable contact member defining therein a main current path for the current flowing under normal-service conditions through said movable contact member in the closed-circuit position thereof, said device comprising:

a magnetic circuit energized by the current flowing through said circuit interrupter and having closely elongated conducting induction-plate means extending a length parallel with and adjacent to said path betweensaid pole faces in said gap means when said movable contact member is in said closedcircuit position, said induction-plate means being movable with said movable contact member and electrically connected thereto in shunting relation so that the rising of said fault current and the resulting rising of the magnitude of said magnetic field induce in said induction-plate means a secondary current linking said magnetic field and tending to repel said induction-plate means from said gap means to cause said separation of said contact means.

2. A device according to claim 1, said magnetic circuit having a loop-shaped configuration surrounding said movable contact member.

3. A device according to claim 2, said movable contact member and said induction-plate means forming a unitary structure having a generally T-shaped cross section.

4. A device according to claim 1, said movable contact member being comprised of a bridge contact guided for translatory motion perpendicularly to said longitudinal direction and to the direction of said magnetic field.

5. A device according to ,claim 1, said movable contact member comprising a relatively wide generally bar-shaped bridge-type contact member defining said path and a relatively thin generally keel-shaped projection depending therefrom and constituting said induction plate means.

6. A device according to claim 1, the longitudinally opposed end portions of said induction plate means being electrically connected to said movable contact member, the intermediate portion of said induction plate means being electrically insulated from said movable contact member.

7. A device according to claim 1, said induction plate means comprising a portion of ferromagnetic material.

such a manner that the energization of said magnetic circuit by said current flowing through said current interrupter produces an attraction force acting on said armature means and tending to separate said contact means through said mechanical connection means.

10. A device according to claim 9, said mechanical connection means comprising lost-motion means.

11. A device according to claim 10 comprising resilient contact pressure means tending to close said contact means to take up the lost motion of said lostmotion means.

12. A device according to claim 9, said movable contact member carrying main contact means, said device further comprising arcing contact means cooperating with are extinguishing means and connected to said movable contact member by lost-motion means. 

1. An electromagnetic repulsion device causing under predetermined fault current conditions the separation of the separable contact means of a circuit interrupter by imparting motion to a movable contact member of said contact means, said movable contact member defining therein a main current path for the current flowing under normal-service conditions through said movable contact member in the closed-circuit position thereof, said device comprising: a magnetic circuit energized by the current flowing through said circuit interrupter and having closely spaced apart confronting pole faces defining therebetween adjacent said movable contact member gap means in such a manner that said current flowing through said circuit interrupter induces in said gap means a magnetic field directEd substantially transversely of the longitudinal direction of said current path in said movable contact member; and elongated conducting induction-plate means extending a length parallel with and adjacent to said path between said pole faces in said gap means when said movable contact member is in said closed-circuit position, said induction-plate means being movable with said movable contact member and electrically connected thereto in shunting relation so that the rising of said fault current and the resulting rising of the magnitude of said magnetic field induce in said induction-plate means a secondary current linking said magnetic field and tending to repel said induction-plate means from said gap means to cause said separation of said contact means.
 2. A device according to claim 1, said magnetic circuit having a loop-shaped configuration surrounding said movable contact member.
 3. A device according to claim 2, said movable contact member and said induction-plate means forming a unitary structure having a generally T-shaped cross section.
 4. A device according to claim 1, said movable contact member being comprised of a bridge contact guided for translatory motion perpendicularly to said longitudinal direction and to the direction of said magnetic field.
 5. A device according to claim 1, said movable contact member comprising a relatively wide generally bar-shaped bridge-type contact member defining said path and a relatively thin generally keel-shaped projection depending therefrom and constituting said induction plate means.
 6. A device according to claim 1, the longitudinally opposed end portions of said induction plate means being electrically connected to said movable contact member, the intermediate portion of said induction plate means being electrically insulated from said movable contact member.
 7. A device according to claim 1, said induction plate means comprising a portion of ferromagnetic material.
 8. A device according to claim 1 further comprising stationary conductor means supplying current to said contact means and surrounded by said magnetic circuit to cause the energization thereof.
 9. A device according to claim 1 comprising armature means spaced apart from said magnetic circuit when said movable contact member is in said closed-circuit position; and mechanical connection means connecting said armature means to said movable contact member in such a manner that the energization of said magnetic circuit by said current flowing through said current interrupter produces an attraction force acting on said armature means and tending to separate said contact means through said mechanical connection means.
 10. A device according to claim 9, said mechanical connection means comprising lost-motion means.
 11. A device according to claim 10 comprising resilient contact pressure means tending to close said contact means to take up the lost motion of said lost-motion means.
 12. A device according to claim 9, said movable contact member carrying main contact means, said device further comprising arcing contact means cooperating with arc extinguishing means and connected to said movable contact member by lost-motion means. 